1. Field of the Invention
The present invention relates to a vacuum interrupter having an adverse effect of an eddy current.
2. Description of the Prior Art
It has been well known that an interruption characteristic is improved by applying a vertical magnetic field in parallel to an arc of a vacuum interrupter.
FIGS. 1(a), (b) is a schematic view of a conventional vacuum interrupter showing the principle of a structure of an electrode wherein the reference numeral (1) designates a conductive rod; (20) designates a coil electrode which has an arm projected radially from a base of the conductive rod (1) and which continues through one coil twin and is connected by means of a connection (21) to a main electrode (3). The coil electrode (20) is shown in the form of the one turn-coil, however, plural coil electrodes (20) can be provided in the back side of the main electrode (3). The reference (A) designates an arc formed between the main electrode and a counter electrode (not shown) and the reference (i) designates a current resulted by the arc and the direction of the current is shown by the arrow line. The aforementioned elements are vacuum tightly installed in a vacuum container (not shown) so that each other end of the conductive rods extend exterior to the container.
The operation of the conventional interrupter will be illustrated. The arc (A) is formed on the main electrode (3) and the current (i) is fed through the connection (21) and the one turn-coil formed by the coil electrode (20) to the conductive rod (1) whereby a magnetic field in parallel to the arc (A) is generated. It has been considered that the arc having a low arc voltage and uniform distribution can be obtained by the interaction between the magnetic field and the arc.
Because of the above-mentioned structure of the electrodes, a reinforcing part for spacing the main electrode (1) and the coil electrode (20) is needed and the coil electrode (20) must have a rigid structure to be durable to an electromagnetic force caused by the large current and a mechanical shock caused in the switching whereby a large thickness unnecessary for electrical purposes is required for the coil electrode which is usually made of copper having high conductivity. The magnetic field generated by the coil electrode is perpendicular to the main electrode (3) whereby an eddy current is passed in the main electrode (3) to reduce the magnetic field generated by the coil electrode (20) by the magnetic flux in the reverse direction caused by the eddy current. The desired results have not been attained. Thus, in the conventional practical vacuum interrupter, many grooves for eddy current prevention are formed on the main electrode (3) to cause inferior mechanical strength of the main electrode. Therefore, a reinforcing part made of a non-magnetic high resistant metal is needed. The two layer structure of the main electrode and the coil electrode with the reinforcing part should have high accuracy and accordingly, the fabrication and the fixing process are complicated causing great expense. In spite of the complicated and expensive structure, the effect of the electrodes is not satisfactory. The intensity of the magnetic field is reduced for the distance of the coil electrode from the surface of the main electrode which generates the arc because the coil electrode is formed on the back side of the main electrode. In order to give the intensity of the magnetic field required for the arc, it is necessary to generate the magnetic field having high intensity by the coil electrode. Therefore, the adverse effects of the electromagnetic force and the eddy current are severe. The serious disadvantages have been found.